Speaker enclosure



Jan. 23, 1968 Filed Feb. 1, 1967 E-. S. TRANSUE SPEAKER ENCLOSURE 2 Sheets-Shem 1 IN VENTOR.

. EDGAR S. TRANSUE ATTORNEY 3 v m wE III I.

E- TRANSUE SPEAKER ENCLOSURE 2 Sheets-Sheet 2 v Jan. '23, 1968 Filed Feb. 1, 1967 I NVEN TOR. EDGAR s. TRANSUE BY @m/Q QM ATTORNEY United States Patent 3,365,021 SPEAKER ENCLOSURE Edgar S. Trausue, San Diego, Calif., assignor to Jos.

Schneider Feinwerktechnik G.m.b.H., Bad Kreuznach, Rhineland, Germany, a corporation of Germany Filed Feb. 1, 1967, Ser. No. 613,276 9 Claims. (Cl. 181-31) ABSTRACT OF THE DISCLOSURE This invention relates to a speaker enclosure that places a diaphragm speaker in a smaller enclosure having compression baffles on opposite sides to control the diaphragm movement in forward and backward directions and which smaller enclosure is placed in a larger enclosure having sound-delaying baffles that prevent cancellation of bass sound waves in the rear wave.

Background of the invention The principal reason for a speaker enclosure or baflle is to separate the sound radiated vfrom the rear of a speaker diaphragm so that it does not cancel the radiation from the front of the diaphragm. These two sound sources differ by a 180-degree phase relationship. A characteristic of sound waves is that the lower the frequency the longer the wave lengths and the more circular the radiation. Low frequency tones produced from both the front and rear of the loudspeaker diaphragm meet at the edge of the diaphragm where, being exactly out of phase, they cancel each other. The result is little or no bass. If the low frequency wave is given an opportunity to build up in space before cancellation occurs, then an improvement in low frequency sound propagation will result because it takes a comparatively long time for a low frequency wave to become established in the air. Out of the need to prevent cancellation of the bass sound waves, two basic types of direct radiator enclosures have been developed, namely the infinite baflfle enclosure and bass reflex enclosure.

An enclosure or baflie is a separator that increases the distance between the front and the back of the speaker diaphragm to such dimensions that the Wave length of the lowest useful frequency is small in comparison to the distance of separation.

The infinite baflle suppresses the speakers back wave to avoid its cancelling the front radiation. In its original concept the infinite baffle is a rigid wall at least 15 feet square. An example is a speaker mounted through a wall. In a practical sense the wall is folded into a box that totally encloses the rear radiation. The loudspeaker is limited only by its natural resonance; below this point efliciency falls off by 12 decibels per octave.

The bass reflex enclosure is an example of a Helmholtz resonator, that allows the back wave to emerge through a port in phase with the front wave by being stored in the enclosure. The bass reflex is essentially a phase inverter for the low frequencies. At the higher frequencies the system suppresses the rear wave and reverts to an infinite battle system. The bass reflex can be tuned to the resonance of the loudspeaker it is to work with, extending the low frequency response below the natural resonant point of the loudspeaker.

The 12-inch loudspeaker employed in the development of this invention resonated at 28 cycles per second. Using test records it is possible to hear a 40-cycle note. A 30- cycle note is more felt than heard. It is deemed impractical to develop signals below audibility when midfrequency response is much more important thah extremely low frequency response which, in the concert hall, borders upon inaudibility. Few, if any notes are ever played below 30 cycles per second. Additionally, it is difficult to record the last octave. The lowest note of the great organ (32.7 cps.) does not frequently occur in musical compositions.

Presence is determined by middle frequency performance. When middle frequencies are reduced, presence is reduced. When they are increased, presence is increased. Almost every instrument in the orchestra gets below 300 cycles. Only the tympani, bass and snare drums, bass viol, tuba and organ have any range below cycles. The bass drum has harmonics beyond 5000' cycles and the bass viol almost to 10,000 cycles. Helmholtz showed that the distinctive quality or timbre of a complicated sound is determined by the component frequencies that compose it. A bell, for instance, is capable of vibration at an irregular series of frequencies. When the clapper strikes it, these vibrations are all set up at once, and a clangorous sound of many non-harmonically related frequencies is produced. A stretched string, however, vibrates at frequencies that are multiples of the fundamental frequency. In orchestra music the string sections, Woodwinds, brass and percussion are frequently being heard simultaneously creating an imposing array of non-harmonically related frequencies and energies.

The present invention places a heavy, balanced air load upon both the front and the rear of the loudspeaker diaphragm in contrast to the infinite battle and bass reflex systems that offer merely a decorative grill of plastic, wood, cloth, or metal, and atmospheric pressure against the front of the loudspeaker. The air mass load in the infinite baflie and the bass reflex enclosure offers a relatively heavy load on the rear of the loudspeaker diaphragm. When the diaphragm reverses itself and moves forward it will not find the heavy load but will instead find a very compliable open space. It will therefore move forward much more easiy than backward. For the same driving force the diaphragm will tend to move more in the forward direction than in the rear direction. When this occurs there is an undesirable nonlinearity of response. Any irregularity of performance (intermodulation) of the diaphragm in reproducing the low note will adversely affect the high note, because the high note, in a sense, rides on top of the low note. The high note is thus modulated by the low note. Linearity exists in a system when that system is as free to move in one direction as it is to move in the opposite direction. Linearity permits more usable power to be obtained from the system.

In order to render the invention more comprehensible other basic facts will be reviewed briefly. Sinsusoidal waves of sound are produced when the diaphragm of a radio or phonograph loudspeaker moves smoothly back and forth as if it were driven from a crankshaft vibrating at a frequency of 12 complete oscillations a second. Any system, electrical or mechanical, acquires momentum when it is energized, particularly when it is energized at a high level. Reproducing systems want to keep on vibrating after the stimulating waveform has stopped, producing a sort of echo or hangover of the original sound. Damping is necessary for a speaker system not only to prevent it from generating a tone at its own resonant frequency, but to minimize hangover of the waveforms passing through it. Once a mechanical device like a speaker is put into motion, it tends to continue in motion after the stimulus has stopped. A high amount of damping is therefore necessary for a speaker to reproduce fast decays faithfully. The highly damped speaker has the finest transient response and is preferred by critical listeners. Transient response of a loudspeaker is the ability of a loudspeaker to follow sharp, sudden signals, such as 3 drum beats, and to stop producing the sound as soon as the signal stops.

In order to obtain high efficiency it is beneficial to damp the impedance peak of the loudspeaker for purposes of'allowing more power to be admitted to the loudspeaker. Impedance is the property of blocking or stopping something. A high impedance permits only small values of current to flow, and low impedance allows large values of current to flow. By damping the impedance peak of the loudspeaker more uniform power input and more uniform power output are obtained. Useful acoustic power will be radiated without power being wasted in mechanical resistance.

The moving system of the loudspeaker has a certain amount of inertia (motional impedance) that is reflected back to the loudspeaker terminals due to the movement of the diaphragm. The greater part of the power delivered to the loudspeaker by the amplifier is expended in the voice coil resistance and merely heats the voice coil, whereas only a relatively small proportion is radiated as sound due to the motional impedance. The voice coil spends much more of its driving force moving the diaphragm than the air in contact with the diaphragm because of the difference in the density of the material of which the diaphragm is made and that of the air. In the loudspeaker from which the voltage has suddenly been removed, there is no voltage driving the voice coil. It immediately stops acting as a motor. However, due to the inertia of the moving diaphragm, the system continues to vibrate. When a suddenly applied electric signal is fed to the voice coil it takes a certain time for the inertia of the voice coil and its diaphragm to be overcome before the system can begin to move. This time delay between action and reaction constitutes a form of transient distortion.

Resonance damping allows greater power into the loudspeaker. Loudspeakers are most efficient at resonance. Low frequency efficiency is found with low resonant frequency. The ability of a low frequency speaker to reproduce low bass is limited by its resonant frequency. Below the resonant point of the loudspeaker the low frequency output drops at the rate of 12 decibels per octave. When the cycle to be heard is the same as the resonant frequency of the loudspeaker diaphragm, the speaker begins vibrating at its natural frequency simultaneously and for a period after the desired cycle has passed, drowning out frequencies close to this cycle. The ear hears this as distortion. If this occurred at lower frequencies that border on the lower threshold where the ear barely hears any sound (30 to 40 cycles) it would not be so objectionable.

The acoustic power output of a loudspeaker system is proportional to the displacement of the diaphragm in a given short period of time, for the more the diaphragm moves and the faster it moves, the more air will be set in motion.

Summary of the invention It is therefore an object of this invention to provide a new and improved speaker enclosure.

It is another object of this invention to provide a new and improved speaker enclosure that simultaneously controls the forward and backward movement of the loudspeaker diaphragm.

It is another object of this invention to provide a new and improved speaker enclosure for direct radiator loudspeakers that is capable of faithfully reproducing sounds in the low part of the audible frequency range as well as giving excellent transient response and substantially increasing the volume of sound produced.

It is another object of this invention to provide a new and improved speaker enclosure that provides an equalized compression force on the speaker diaphragm in forward and backward movements.

It is another object of this invention to provide a new and improved speaker enclosure that provides improved phasing of the forwardly and rearwardly produced sound waves. 7

My invention comprises a diaphragm speaker enclosure having compression bafiies' on opposite sides to control movement of the sound producing diaphragm in the forward and backward directions. The compression box is en closed by a larger box shaped enclosure in which the speaker board forms the front side of the larger enclosure and the compression box. The speaker board has an opening for passing forward sound waves generated by the speaker diaphragm. A rim or frame is inserted be tween the opening and the forward compression baflie to direct the air pressure into the forward compression battle and prevent escape of air pressure across the speaker board.

Sound delaying baffles are positioned adjacent to either side of the compression box and fit between the top and bottom of the larger enclosure in a position essentially parallel to the compression box and the sides of the larger enclosure but spaced from the speaker board, for the purpose of creating a circuitous route for sound waves to follow before emerging from the back of the enclosure. This lessens cancellation of the low frequencies. The back panel is fitted between the two baffies. The sound delaying bafiies serve as an element in the crossover system by attenuating the higher frequencies. The low frequencies flow readily out of the rear of the loudspeaker, around the bafiles, and out into space, because low frequencies readily diffract or bend around corners. Frequencies around 5,000 c.p.s. flow readily out of the loudspeaker, around the bafiies, and out into space. Frequencies above 5,000 c.p.s., however, will not travel around bends as easily and therefore are absorbed or lost in the maze of the enclosure.

Certain features of this invention make direct use of my speaker diaphragm compression baffle for the purpose of improving its efficiency and extending its benefits to include the backward sound wave output of the loudspeaker diaphragm. Over excursion of the loudspeaker diaphragm and cone breakup, which results in phase differences between the movements of various sections of the cone, are controlled by compressing air between the baflie and the loudspeaker diaphragm. The piston of a loudspeaker should remain a rigid piston all the time. Unfortunately it tends to breakup in the mid-frequency range as various sections of the diaphragm resonate. This not only produces resonant peaks at this mid-frequencies, but keeps the piston from being really-efficient at the low frequencies. As the frequency of reproduction of a speaker diaphragm goes up the energy becomes more tightly beamed, with the result that the overall angular performance of the diaphragm drops off. This effect is offset by the compression bathe that increases the density of medium through which sound must pass, slowing up ends of the wave front causing them to twist from plane waves to spherical waves, thereby increasing angular performance to degrees. At the rear of the speaker the compression baffle contributes to minimizing cancellation of the low frequencies by decreasing the velocity of sound issuing from the back of the enclosure.

In the preferred embodiment of the invention provision is made for an air space within the enclosure of suflicient size to envelop the compression box in order to not restrict necessary movement of the loudspeaker diaphragm. An opening of appropriate size in the back panel relieves internal pressure against the loudspeaker diaphragm, permitting an enclosure of medium size, as well as preventing the restricted sound that would otherwise result.

Other objects and advantages of my invention will be apparent in the following more detailed description and in the drawings in which like reference numerals identify like parts of the various figures thereof and wherein,

FIGURE 1 is a perspective front view of the embodiment of my invention.

FIGURE 2 is a perspective rear view with parts broken away of the embodiment of my invention.

FIGURE 3 is a cross sectional view taken along lines 3-3 of FIGURE 1.

Referring now to the drawing, there is provided a large, box shaped first speaker enclosure having sides 14 and 18 and a top 20 and a bottom 22. The first enclosure has a back panel 16 that partially covers the rear of the enclosure and a front panel 12 that is also a speaker board, as will become more apparent hereinafter. A second, smaller speaker enclosure 91, that functions as a compression box and houses a diaphragm speaker 32, has sides 98 and 100 and a bottom 99. The forward side of the second speaker enclosure 91 abuts and is secured to the speaker board 12. The upper surface of sides 98 and 100 are secured to the under surface of the top 20 of the first enclosure 10. The bottom surface 99 of the second enclosure 91 is spaced a substantial distance from the bottom 22 of the first enclosure.

The speaker 32 is secured to and supported by the speaker board 12 and an opening 34 through the speaker board 12 that passes forward sound waves generated by the speaker diaphragm. A rim or frame 61 comprising members 60, 62, 64 and 68 frame the opening 34 and functions to direct the forward sound waves to the compression means or baffle 28 and prevent the forward sound waves from escaping along the surface of the speaker board 12. The forward speaker compression bafiie 28 is secured directly against the frame 61 in the manner shown in FIGURES 1 and 3. The width and height of the baffle 28 is substantially the same size as the frame 61 in order to not protrude beyond the sides of the frame 61. The forward speaker compression baffle 28 comprises a speaker blast baffle 36 and two rows of compression slats that overlap and are spaced apart to compress the air between the moving speaker diaphragm and the compression means 28, while at the same time, allowing the sound to escape at substantially right angles through spaces '70, 72, and 74. Longitudinal members 38, 50, 58, 40, 41, and 43 support and space the upper and lower ends of the rows of slats and the speaker blast baffie 36. The rows of slats generally comprise slats 42, 44,- and 46 in the front row and four slats 52, 56, and

66 in the second row adjacent the frame. The slats are spaced creating spaces, for example, space 48 and space 54, which spaces are overlapped by the slats in the adjacent row. This overlapping of the slats and the blast baffle 36 creates a restrictive path for air moving therethrough that compresses the air between the moving diaphragm and the compression means 28. Because of this compressive resistance in front of the speaker, the vibrating speaker diaphragm is better able to remain intact, avoiding a defect known as cone break-up. Additionally, the straight forward issuance of sound called speaker blast is prevented.

A second or rear speaker compression bafiie 30 is secured to andencloses the rear opening of the second enclosure 91. As maybe seen, the second speaker compression baffle 30 has a speaker blast baffie 80 with two rows of slats having the same configuration and construction previously described relative to the first speaker compression baffle 28. Rearward sound waves emanating from the speaker diaphragm in its rearward movement are similarly compressed with the rearward sound waves leaving the compression box 91 through openings 86, 88, and 90. Thus the rear speaker compression baflle 30 functions to direct the rearward sound waves in an angle substantially normal to the normal direction of projection of the rearward sound waves so that the sound waves follow a path substantially as identified by the dotted line 130.

The first enclosure 10 has mounted therein delay panels or baffles 24 and 26 that are secured to the inner surface of the top 20 and bottom 22 of the enclosure 10. The delay baflies 24 and 26 abut the rear panel 16 forming an enclosed volume between the rear speaker compression baffle 30 and the baffles and rear panel. It should be recognized that an additional volume exists underneath the compression box 91 between bottom 99 and the bottom 22, which with aperture 122 provides sufficient air volume that the speaker diaphragm is not restricted in its reverse movement to any greater extent than the diaphragm is restricted in its forward move ment. The delay baffles 24 and 26 are spaced a substantial distance from the speaker board 12 creating a circuitous path 130 for the rear sound waves, which circuitous path provides a given delay that causes the low frequency sound waves to leave the rear of the speaker enclosure 12 through the rear opening in phase with the forward sound waves generated by the speaker 32. The small aperture 122 in the bottom of panel 16 permits the free flow of air into and out of the volume of the speaker enclosure 10 while having a sufficiently small size to restrict the passage of sound waves therethrough, that could interfere with the sound waves following the circuitous path 130.

As structural details, frame members 102, 104, 106, 130, 132, 114, and 116 function as joints for securing the structure together. The structure can be joined by cementing, gluing, nailing, or using screw fasteners, or the like. A layer of compressible foam or similar type compression material 112 is placed between the rear panel 116 and the frame members 104, 108 and to reduce possible vibration of panel 16.

An aperture 118 is provided in the speaker baffle 12 for coacting with a higher frequency speaker 120 such as a tweeter or the like.

In operation, the diaphragm of the speaker 32 generates forward and rearward sound waves in a normal manner. The sound waves are projected into the forward and rearward speaker compression bafiles 28 and 30. The speaker compression baflle 28 reduces speaker blast and both baflies provide forward and rearward diaphragm compression on the diaphragm of the speaker 32. The sound Waves emanate from the forward and rearward speaker compression baffles 28 and 30 as previously described. The rearward sound waves are directed along a path around the delay baffles 24 and 26 and out the opening so that the low frequencies are substantially in phase with the forward low frequency sound waves generated by the speaker diaphragm. The tweeter or high frequency speaker 120 operates in the normal manner. Aperture 122 permits free flow of air into the cavity surrounding the compression box 91 thus providing equalized pressure on each side of the compression box. Thus the speaker diaphragm is subjected to the same identical compression forces in its forward and rearward excursion movements. This structure and operation satisfies the previously described problems in speaker enclosures and thus makes it possible to use a less efficient or less expensive speaker in a relatively small size speaker enclosure and yet faithfully reproduces the sound.

The foregoing is considered illustrative only of the principles of my invention. Since numerous modifications and changes will readily occur to those skilled in the art, it is desired to not limit the invention to the exact construction and operation shown and described and thus, all suitable modifications and equivalents that may be resorted to are believed to fall within the scope of the invention as claimed.

Having thus described my invention, what I now claim is:

1. A speaker enclosure capable of providing equalized compression pressure on a speaker diaphragm comprising in combination,

i3. first box shaped enclosure having a front panel for covering the front side of said enclosure and a rear panel that partially covers the rear side of said enclosure leaving a part of said rear side open,

a second smaller compression enclosure positioned in said first enclosure for enclosing a diaphragm type speaker,

the front side of said second enclosure abutting said front panel of said first enclosure with the bottom side of said second enclosure being spaced a substantial distance from the bottom side of said first enclosure,

an opening in said front panel for passing forward sound waves generated by a speaker diaphragm in said second enclosure,

frame means secured to the outer surface of said front panel and framing said opening for directing said forward sound waves,

a first speaker diaphragm compression means mounted on said frame means and a second speaker diaphragm compression means covering the rear side of said second enclosure for pressurizing sound waves generated by said diaphragm,

sound delaying bafile means positioned in said first enclosure and abutting said rear panel for creating an internal cavity substantially surrounding the sides and front of said second speaker diaphragm compression means for providing a circuitous path for the back directed sound waves created by said speaker to pass through the open portion of the rear side of said first enclosure, and

a small aperture means in said rear panel for allowing free flow of air into said internal cavity.

2. A speaker enclosure as claimed in claim 1 in which,

said first and second speaker diaphragm compression means comprises,

redirecting means for changing the direction of said forward and back directed sound waves to a direction substantially parallel with said front and back panel.

3. A speaker enclosure as claimed in claim 1 in which,

said first and second speaker diaphragm compression means comprises,

a plurality of spaced and overlapping slats positioned in the path of said forward and back directed sound waves for changing the direction of said sound waves to substantially a normal angle to the direction of the sound waves leaving said diaphragm.

4. A speaker enclosure as claimed in claim 1 in which,

said panel means comprises,

a pair of wall panels extending from the top side to the bottom side of said first enclosure and being positioned a spaced distance between the sides of said second enclosure and the sides of said first enclosure,

each of said panels abutting a respective side of said rear panel,

the rear side of said first enclosure being open between said panels and said sides of said first enclosure,

and said second speaker diaphragm compression means including redirecting means for directing said back directed sound waves toward the space between said wall panels and the sides of said second enclosure and said redirected sound waves passing out of said first enclosure in the space between said wall panels and the sides of said first enclosure.

5. A speaker enclosure as claimed in claim 4 in which,

said aperture means comprises an aperture positioned near the bottom of said rear panel adjacent said space between the bottom of said second enclosure and the bottom of said first enclosure,

and said aperture being sufiiciently small to prevent the passage of a significant portion of said back directed sound waves therethrough.

6. A speaker enclosure as claimed in claim 1 in which,

said panel means comprises,

a pair of wall panels extending from the top side to the bottom side of said first enclosure and being positioned a spaced distance between the sides of said second enclosure and the sides of said first enclosure,

each of said panels abutting a respective side of said rear panel,

and the rear side of said first enclosure being open between said panels and said sides of said first enclosure.

7. A speaker enclosure as claimed in claim 1 in which,

said first and second speaker diaphragm compression means comprises,

a plurality of rows of slats,

said slats in respective rows being spaced one from another with said slats of the adjacent rows overlapping all of the spaces between the slats of the next said adjacent rows,

and a single bafi'le lying outwardly of the last row of slats and overlapping all of the spaces between the slots of the last mentioned row.

8. A speaker enclosure as claimed in claim 7 in which,

said panel means comprises,

a pair of wall panels extending from the top side to the bottom side of said first enclosure and being positioned a spaced distance between the sides of said second enclosure and the sides of said first enclosure,

each of said panels abutting a respective side of said rear panel,

and the rear side of said first enclosure being open between said panels and said sides of said first enclosure.

9. A speaker enclosure as claimed in claim 8 in which,

said aperture means comprises an aperture positioned near the bottom of said rear panel adjacent said space between the bottom of said second enclosure and the bottom of said first enclosure,

and said aperture being sufficiently small to prevent the passage of a significant portion of said back directed sound waves therethrou-gh.

References Cited UNITED STATES PATENTS 2,979,150 4/1961 Irby 181-31 3,169,601 2/1965 Smith 181-31 3,239,028 3/ 1966 Murray 181-31 3,340,956 9/ 1967 Owen 181-31 STEPHEN J. TOMSKY, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,365,021 January 23, 1968 Edgar S. Transue It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, lines 3 to 6, for "Edgar S. Transue, San Diego, Calif., assignor to Jos. Schneider Feinwerktechnik G.m.b.H., Bad Kreuznach, Rhineland,

Germany, a corporation of Germany" read Edgar S. Transue, 4544 Louisiana Street, San Diego, Calif. 92116 Signed and sealed this 8th day of April 1969.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

